In a sheet stacking apparatus, sheets are sequentially transported horizontally to a position above a stacking area and unloaded vertically to form a stack beneath the apparatus. Each sheet is transported horizontally by laterally spaced apart, longitudinally extending conveyors which support longitudinal edges of the sheet. Such a sheet stacking apparatus operates satisfactorily as long as the width of the sheet between the conveyors is not excessively wide to cause sagging of the sheet. Excessive sagging of the sheet can cause undue bending stress on the sheet or excessive friction or binding at the sheet edge along the conveyor rollers, or possibly cause the sheet to fall through the conveyors before reaching the stacking area. For a wide sheet, it is particularly difficult to support the mid-span of the sheet since any support beneath the sheet must be removed or relocated so as not to interfere with the stack, or the sheet unloading operation to form the stack.
It would be desirable to provide a stacking apparatus which was operable for both narrow sheets and wide sheets and which supported a mid-span of a wide sheet during transporting of the sheet to the stacking area. It would be desirable to provide a support mechanism which is not located such as to require a complex retraction to prevent interference with the forming of the stack. It would be desirable to provide a sheet stacking apparatus which could effectively stack wide sheets of thin gauge material without undue bending or sagging of the sheet.